API stand for application programming interface, which is a source code interface of a computer application that supports requests of a computer program. And a API can be compiled when an application is built, instead of a low level description of how data is laid out in memory by a ABI (application binary interface).


"The term API is used in two related senses:
  • A coherent interface consisting of several classes or several sets of related functions or procedures.
  • A single entry point such as a method, function or procedure."
http://en.wikipedia.org/